Question

The activity of the radioactive sample drops to 1 / 64 of its original value in 2 hr find the decay constant ?$\left(\lambda \right).$

• A. $\left(\lambda \right)=1.079h{r}^{-1}$
• B. $\left(\lambda \right)=1.579h{r}^{-1}$
• C. $\left(\lambda \right)=2.079h{r}^{-1}$
• D. $\left(\lambda \right)=2.579h{r}^{-1}$

Answer 1

Answer: (C)

$\left(\lambda \right)=2.079h{r}^{-1}$

Now, we know $\lambda =\frac{0.693}{halftime}$
here activity drops to $\frac{1}{64}$ in 2 hours. so half life is 20 mins
then using above formula and putting half life time into it we get
Ans-$\lambda =2.579h{r}^{-1}$